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Патент USA US2412782

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Dm. W, 194:6.i
R. 1r. PALMER
2,432,782
WET BULB THERMOMETER AND THERMOSTAT
Filed May 26, 1944
2 Sheets-Sheet l
u
u
Dec. 17, i946.
R. T. PALMER
l
¿M2782
WET BULB THERMOMETER AND THERMOSTAT
Filed May 26, 1944
2 Sheets-Sheet 2
kmq T13-"50NTRÜLÜ
Es@i
Patented Dec. 17, 1946
2,412,782
-UNITED srA'rEs vPii'nzNT oFFlc‘E
v 2,412,782
WET BULB THERMOMETER AND
THERMOSTAT
Robert T. Palmer, Sharon, Mass.
Appllcûtlon May 26, 1944, Serial N0. 537,507
12 Claims. (Cl. 23e-_44)
2
This invention relates to instruments respond
ing to wet bulb temperature changes such as are
commonly known as wet bulb thermometers and
wet bulb thermostats.
_
This application is a continuation-in-»part of
by copending application, Serial No. 428,312, filed
January 26, 1942.
Wet bulb thermostats are desirable for such
duties as regulating air cooling systems in accord
ance with latent heat changes. The usual wet
bulb thermostat is a dry bulb thermometer
utilizing a water soaked wick around its bulb for
obtaining a wet bulb depression through evapora
tive cooling. Such thermostats have not been
' extensively used due to the diiliculties of supplying
the correct amount of water to the wicks and ci’
keeping the Wicks clean in theAA out-of-way
locations such as in ducts, where control thermo
stats are usually located. `
,
For example, in one embodiment of this inven
tion, the humidity of the air determines the power
absorption of a hygroscopic dielectric between turc
condenser electrodes in an electrostatic iield,
While the dry bulb temperature determines in
dependently, the strength of the field between
the electrodes. A humidity increase causes an
incrase in power absorption due to the increased
absorption of moisture by the hygroseopic dielec
tric. A dry bulb temperature increase causes a
bi-metallic element to increase the spacing be
tween the electrodes, thus decreasing the capacity
and the power absorption. The two changes are
so correlated that a meter or a control in the oscil
lator circuit indicates or responds, respectively, to
the prevailing wet bulb temperature.
In another embodiment of the inventiony a
humidity increase in the air may cause the fre
quency oi an alternating electric current to in
This invention provides wet bulb thermostats
and thermometers which do not require water 20 crease, while an increase in the dry bulb tempera
supply and which are electronic in action.
This invention depends in principle, upon the
fact that as shown by standard psychrometric
charts, relative humidities, dry bulb temperatures
ture of the air may cause the frequency to de
crease. The frequency changes are so correlated
that the resultant of the changes indicates the
wet Vbulb temperature of the air.
and wet bulb temperatures are so related that 25 A humidity increase in the air to which a device
embodying this invention is exposed, may also
the relations between any two of these three
cause an impedance change in an electric circuit
variables enable the third to be determined. For
while a dry bulb temperature increase may cause
example, suppose it is desired that a wet bulb
thermostat actuate a control at 70° F. wet bulb 30 an impedance change which is opposite in eiîect
to that caused by the humidity increase. For
temperature. For this wet bulb temperature
example,v a hygroscopic resistor connected in an
Relative
Dry bulb
Percent
Degrees
B0
75
70
60
50
40
77
80
84
88
humidity temperature
electric circuit, decreases in resistance with in
crease in humidity while the resistance of another
resistor in series therewith, is increased with in
crease in the dry bulb temperature.
Objects of the invention are to measure wet
bulb temperatures and to actuate controls in
response to wet bulb temperatures, by electronic
action.
40
The invention will now be described with refer
'I'his invention causes the varying factors of dry
ence to the drawings, of which:
bulb temperature and relative humidity elec
Fis’. 1 is a diagrammatic view of one embodiment
tronically to determine and to indicate wet bulb
of this invention utilizing hygroscopic, book type
temperatures, and to actuate controls at pre
electrodes, the capacity between the electrodes be
determined wet bulb temperatures.
45 ing varied by a bi-metallic element responsive to
A moisture increase in the air to which a device
embodying this invention is exposed, may cause a
dry bulb temperature changes.
frequency or intensity change in electric current
flow while an increase in the dry bulb tempera
condenser having plates coated with hygroscopic
change in current flow. The said current ilows
type condenser of Fig. 1;
Fig. 2 is a diagrammatic view illustrating a
ture may cause an opposite frequency or intensity 50 material and having plates rotated by a bi-metallic
spring, and which may be substituted for the boola
are so evaluated with respect to the values shown
by a psychrometric chart that the resultant fre
quency or intensity of the current is a measure of
the wet bulb temperature of the air.
A
Fig. 3 is a diagrammatic view of a condenser
which may be substituted for the book' type con
denser of Fig. 1, having two sets of rotary plates,
55 one set being rotated by a coiled hygroscopic ele
2,412,782 '
4
3
ment affected by humidity changes and the other
set being rotated by a coiled bi-metallic element
affected by dry bulb temperature changes.
Fig. 4 is a sectional view along the lines 4-4
of Fig. 3;
'
Fig. 5 is a sectional view along the lines 5-5
of Figs. 2, 3 and 6;
Fig. 6 is a diagrammatic view of another em
bodiment of this invention utilizing an induct
ance instead of a condenser for responding to'
humidity changes, the inductance having rela
tively fiat wires coated with hygroscopic material
affected by humidity changes, the inductance be
ing connected by a variometer to the oscillator,
electrodes to the high frequency oscillator I3, an
oscillating high frequency electrostatic iield being
set up between the plates III and I I. The similar
free electrode I4 is placed between the electrodes
I0 and I I and acts to increase the capacity of the
condenser formed by the electrodes II) and Il.
The inner surfacesof the electrodes IIJ and I I
and both surfaces of the electrode I4 may be
coated with a hygroscopic medium such, for ex
ample, as cellulose acetate dissolved in acetone
and applied as a lacquer to the surfaces. The
i moisture absorbed by the coatings varies as the
relative humidity of the air passing between the
electrodes changes. The moisture absorption
the' rotor of the variometer being rotated by a 15 changes the condition of the dielectric between
the electrodes and thereby changes the capacity
coiled bì-metallic spring aiïected by dry bulb> tem
and reactance of the condenser and changes the
perature changes;
power absorbed by the hygroscopic dielectric from
Fig. '7 is a diagrammatic view of one oscillator
the electrostatic ñeld.
circuit which may be employed in the practice of
The moisture absorption of the hygroscopic
20
this invention;
l
dielectric varies conformably with changes in the
Fig. 8 is a diagrammatic view of anotherV oscil
relative humidity of the air. The spacing be
lator circuit which may be employed in the prac
tween the electrodes I0 and` Il varies conform
tice of this invention;
ably with changes in the dry bulb temperature.
Fig. 9 is a diagrammatic view cfa third form
> of oscillator circuit which may be used in the 25 The constants of the apparatus are so chosen as
practice of this invention;
Fig. 10 is a diagrammatic view of another em
bodiment of this invention in which a hygro
scopic resistor is connected in series with a vari
able resistor in the grid circuit of a thermionic
electron tube, the resistance of the variable re
sistor being adjusted by a dry bulb thermometer,
the two resistors being in shunt with a D. C. volt- .
age source;
Fig. l1 is a diagrammatic view or' another em
bodiment of this invention, similar to that of
Fig. 10 except that the voltage source is con
nected in series with the variable resistors;
Fig. l2 is a diagrammatic view of another ema
bodiment of this invention, similar to that of Fig.
10 except that the electron tube is of the cold
cathode type, and the voltage source need .not be
direct current.
by observation of the effects through comparison
with calibrated meters, that the resultant effect
upon the oscillator I3 varies’conformably with
changes in the wet bulb temperature of the air.
The meter I5 connected in the oscillator cir
cuit as will be described, serves to indicate the
wet bulb temperature of the air, and the relay I6
connected in the oscillator circuit, serves to cause
the device to act as a wet bulb thermostat for
actuating controls of humidity changing devices
when the oscillator current reduces a predeter
mined value.
instead of coating the surfaces of the electrodes
with a hygroscopic layer, a dielectric such as
reverted cellulose may be placed between the elec
trodes as disclosed in the Allen Patent No.
1,708,073.
bodiment of this invention, similar to that of Fig.
9 except that instead of the thermostatic element
The oscillator i3 may be of the type disclosed
in said Allen patent, or may be of the types dis->
closed in the Stevens et al. Patent No. 2,231,035,
or may be of the type disclosed in the Terman
varying a capacity, it varies a resistor in series
Patent No. 1,976,904. Suitable circuits whichv
with the hygroscopic resistor;
lFigli is a diagrammatic view of another em»
may be used will be described in the foregoing in
connection with Figs. 7-9.
Fig. 2 discloses a modiiied form oil condenser
which may be used. It is a conventional tuning
condenser having stator plates Il and rotor
plates i3. rThe rotor plates i8 are rotated by a
coiled bi-metallic member I2 such as shown by
Fig. 5 so that increases in dry bulb temperature
Fig, i3 is a diagrammatic view of another em
bodiment of this invention using a relaxation
type, resistance tuned oscillator;
Fig. l5 is a diagrammatic view of another em
bodiment of this invention similar to that of Fig.
l1, except that a resistor, the value of which
varies with temperature, is connected in series in
the grid circuit of they control tube with a resis
tor, the value of which is varied with humidity,
and
-
'
Fig. 16 is a diagrammatic view of another em
bodiment of this invention utilizing an ohmmeter
and a rectiñer bridge circuit energized by alter»
nating current.
-
Referring now to Fig. l, the spaced metallic
plates 10 and l1 form a book type condenser, the
plate Ill being adapted and arranged to be rotated
by the coiled by-metallic member I2 so that the
spacing between the plates increases with in
creases in the dry bulb temperatures, and de
creases with decreases in dry bulb temperatures.
'The capacity of the condenser thus decreases
while its reactance increases, with increases in
dry bulb temperatures, and its capacity increases
while its reactance decreases, with decreases in
dry bulb temperatures.
The plates l0 and Il are connected as opposed
cause reductions in capacity as described in con
nection with Fig. 1. The member l2 is mounted
onv the shaft I9 on which the plates i8 are mount
ed, with its inner end in a slot in the shaft and
its outer end held by the bracket 20 which is at
tached to the case 2l. The plates I‘i and i8 are
coated with hygroscopic material as described in
connection with Fig. l, the overall eiïect being as
in Fig. 1, of the hygroscopic absorption, and of
dry bulb capacity variation, on an oscillator con
nected'to the condenser of Fig. 2, to cause a re
sponse to wet bulb temperature.
Fig. 3 shows another form of condenser which
may be used. Instead of the condenser plates
being coated with hygroscopic material, it has
two sets of rotary plates, one set being rotated
by a coiled hygroscopic tape 22 in the case 23
while the other set is rotated by a coiled bi-me
tallic member as described in connection with
Fig. 2. The humidity changes cause the tape 22
asians:
to rotate the plates more in mesh with the stator
plates Ill to increase the capacity of the con
denser, while the spring I2 rotates the other set
be calibrated to read wet bulb temperatures, and
o1' rotor plates I8 to decrease the capacity of the
condenser. The resultant capacity varies con
ture occurs.
The oscillator'circuit of Fig. 9 includes a re~
the relay I8 may be adjusted to close a control
circuit when a predetermined wet bulb tempera
iormably with wet bulb temperature changes.
sistance tuned oscillator of the type disclosed in
The tape 22 may be a strip of cellulose applied
pages S33-,344 of the June, 1941, issue of Pro
to a strip of lshim brass as disclosed in the
ceedings of the Instituteof Radio Engineers. The
Rolleison Patent No. 2,093,767, and fastened to
tuning condenser 38 has its capacity varied with
the rotary shatt of its associated rotor plates as 10 changes in dry bulb temperature as disclosed in
described above in connection with the support
connection with Fig. 2 so as to decrease the capac
of the Ímember I2 upon the shaft I9.
» ity and increase the reactance upon increase in
The rotor plates 2l could also be rotated by an
dry bulb temperature. The resistance 31 is a
elongated Y hygroscopic element as disclosed in
hygroscopic element. of the type disclosed, for
the Allen Patent No. 1,781,153.
_
15 example, in the December, 1939, issue oi’ the
Fig. 6 illustrates how inductances may be ad
Journal of the National Bureau of Standards, the
justed conformably with relative humidity
changes and dry bulb temperature» changes for
causing resultant effects which vary conform
‘ electrical resistance of which varies conform
ably with changes in the relative humidity of the
air. The effects of the adjustments of the con
ably with wet bulb temperature changes. The 20 denser 36 and the resistance 31 are to change
inductance 125 has its turns coated with hygro
the frequency of oscillation of the tube 35. A
scopic material whereby the distributed capacity
decrease in the impedance of the circuit caused by
varies conformably with relative humidity
a decrease in capacity causes a higher frequency
changes, thus variably tuning theinductance.
oscillation. A decrease in resistance resulting
The inductance 25 is connected to the rotor 25 from an increase in humidity causes a decrease in
winding of the variometer 26, which winding may
frequency. The impedance changes are so ad
be the inductance 21 of Fig. '7, while the oscillator
justed that the frequency meter i5 connected
is connected by the wires 30 and 3| to two wind
across the inductance 3B, may be calibrated to '
ings on the stator of the variometer, which wind
read wet bulb temperatures. The contact 39 on
ings may be the inductances 28 and 29 of Fig. ’1. 30 the scale of the meter is set at the desired con
A coiled lai-metallic member rotates the rotor of
trol point so that the indicator 40 closes a con
the variometer to vary the eil'ect of the induct
trol circuit when a predetermined wet bulb tem
ance 25 upon the field from the oscillator, con- A
formably with dry bulb temperature changes, for
decreasing the coupling conformably with dry
bulb temperature increases and for increasing
the coupling conformably with dry bulb tempera
ture decreases. The over all effect is, as de
`
perature occurs.
The embodiment of the invention illustrated by
Fig. 10 comprises the hygroscopic resistor 5!!
which may be of the type disclosed in the F. W.
Dumore Patent No. 2,285,421, the resistance of
which decreases conformably with humidity in
creases in the air to which it is exposed. The
scribed in connection with Figs. 1-5,v_that the os~l
cillator is modliied coniormably with Wet bulb 40 resistor bil is connected in series with the vari
temperature changes.
able resistor bi, the contact arm ‘52 of which is
'i discloses an oscillator circuit of the type
varied by the bellows 53 connected by the tube
disclosed in said Stevents et al. patent and in
5i with the dry bulb thermometer b5.
which a vacuum tube oscillator has an output
The resistors 5B and bi in series are connected
-voltage which falls with increase in load caused
in shunt with the D. C. voltage source 58 and
by increased power absorption between the elec»
with the control grid circuit of the thermionic
trodes it and ii, which increased power absorp
tube b1.
tion is caused by increase in the moisture ab
The energizing winding of the relay E8 is con
sorbed in the dielectric on the electrodes l0, II,
nected to the anode 59 of the tube 51'and to
and it. lTi‘he decrease in voltage is indicated by
the junction point of the resistor 5I! and one
the meter i5.
‘bi-metallic member i2 acts as previously
described, to increase the spacing between the
electrodes
and II, and thereby to decrease the
power absorption, upon increase in dry bulb tem- f
perature. The meter I5 responds to the differ
ences in power absorption due to moisture ab
sorption and separation of the electrodes, and
may be calibrated to indicate the resultant wet
bulb temperatures.
The relay I6 connected in series with the meter
I5 is adjusted so that it releases its armature 33
to close a control circuit when a, predetermined
wet bulb temperature occurs.
side of the potentiometer 6I. The anode 59 is
also connected 'through the resistor 64 to the con
tact arm 62 of the potentiometer 6I, the other
side of which is connected to the positive side of
the B supply source S3. The minus side of the
source 63 is connected to ground.
The relay 58 is connected in a bridge circuit
in the tube anode circuit and when the poten
tiometer 6I is adjusted until the "relay contacts
>swing wide open, the bridge circuit is balanced.
An increase in voltage at the grid of the tube
will cause the bridge circuit to unbalance and
the relay contacts to close. Such a voltage in
crease will be caused by an increase in wet bulb ~
The oscillator circuit illustrated by Fig. 8 is of 65 temperature,
the resistance of the resistor 50
the type disclosed in said Termen patent and has
a vacuum tube oscillator 3€, the anode current
of which increases conformably with the power
decreasing conformably with humidity increases
and the effective resistance of the resistor El in
creasing conformably with dry bulb temperature
absorption caused by moisture absorbed by the
dielectric between the condenser electrodes I0 70 increases. The constants of the circuit are so
selected that the bridge circuit is unbalanced to
and II. The bi-metallic element I2 acts to de
crease the effect of this loss upon increases in dry
bulb temperature by increasing the spacing be
tween the electrodes. The meter I5 which in
thisl case, preferably is a milliammeter, may thus
close the relay contacts when a predetermined
wet bulb temperature occurs.
‘
The embodiment of the invention illustrated
by Fig. 11 is similar to that of Fig. 10 except that
lno bridge circuit is included in the anode circuit
2,412,782
of the thermionic control tube, the circuit being
balanced by auxiliary variable resistors in the
anode and grid circuits. The common elements
of Figs. 10 and 11 have been given the same ref
erence characters.
and which may be calibrated in terms of wet bulb
temperatures.
Fig. 15 illustrates a control circuit similar to
that of Fig. 11 except that no hygroscopic resistor
is used.
The resistor 9d is oi’ a metal such as
platinum or- nickel, the resistance of which in
creases with increase in temperature. The re
sistor 9_5 in series therewith has its contactarm
adjusted by a coiled hygroscopic element 9B such
85 and the D. C. voltage source 55 are connected
in series across the grid circuit of the tube 55. 10 as that illustrated by Fig. 4 so that increases in
humidity cause decreases in the effective resist
The variable resistor 66 is connected in series
ance of the resistor 95. The sum: of the resist
with the anode 59, the energizing winding of the
ances of the two resistors determines the po
relay' 55 and the Bl supply 63. The resistors 55
tential on the grid of the tube 5l as described in
-and 86 are adjusted to provide that the contacts
connection with Fig. 11, the tube passing suin
of the relay 58 close at a predetermined wet bulb
cient anode current to actuate the relay 58 at a
temperature.
selected wet bulb temperature.
The tube 51 of Figs. 10 and 11 may be of the
Fig. 16 illustrates a control circuit in which no
so-called high vacuum type, or maybe of the
vacuum tube is necessary. The A. C, source |00
-gaseous type in which a ñash over occurs at a
may be 60 cycle alternating current. It is con
predetermined grid potential.
nected by the wire iûi to the resistor |52, the
The embodiment of the invention illustrated
by Fig. l2 uses a cold cathode tube, the cathode _ contact arm |03 of which is moved by the bellows
|04 of the dry bulb thermometer |05. The hy
69 of which is connected to one side of the volt
groscopic resistor |06 is connected by the contact
age source 69 which may be A. C. or D. C. The
arm |03 and to one side-of the input of the full
other side of the supply 69 is connected to the
Wave, copper oxide rectifier lû'l. The other side
hygroscopic resistor 50 which is in series with
of the input of the rectiñer is connected by the
the variable resistor 5|, the balancing resistor
wire |08 to the other side of the source |00. The
15 and the starting anode 1| of the tube El. The
output of the rectifier is connected to the ohm
energizing winding of the relay 58 is connected
meter
or voltmeter |09.
30
in series with the said other side of the source
The resistance of the hygroscopic resistor |06
59 and with the anode 'i2 of the tube 6T. With
decreases with increase in humidity while the re
.such a cold cathode tube, anode current iiows
sistance of the resistor |02 increases with increase
when the starting the anode is raised to the igni
in dry bulb temperature. The constants of the
tion potential. The constants of the circuit may
circuit can be so chosen and the meter |09 so cali
be chosen so that when a predetermined wet bulb
brated
that it reads wet bulb temperatures, and its
temperature occurs, the sum of the resistances
pointer Ilil closes a circuit at a predetermined
of the resistors 50 and 5| decreases to permit
wet bulb temperature to actuate a relay.
the starting anode 7| to be charged from the
The impedance of an electric circuit is made
source 69, to the ignition potential.
up
of the resistance and of the capacitive and in
40
The oscillator circuit of Fig. 13 includes a re
ductive reactance of the components of the circuit.
sistance tuned oscillator similar to that of Fig. 9,
Varying one or more of these as described in the
except that instead of the dry bulb lthermostatic
foregoing,
varies the electrical impedance.
element varying a condenser, it varies a resistor
In the annexed claims, “conformably” means
in series with the hygroscopic resistor. The re
in proportion. For example, a humidity increase
sistance of the hygroscopic resistor 3l decreases
from minimum to maximum may cause a resist
with increase in humidity. The resistor 85 in
ance to decrease from maximum to minimum, and
series with the resistor 8| has its resistance in
a dry bulb temperature increase from minimum
creased with increases in dry bulb temperature. by
to maximum may cause a resistance to increase
the expansion of fluid from the thermometer 83
from minimum to maximum.
into the bellows 82 which shifts the contact arm
The devices referred to in the annexed claims
Bi of the resistor 86. Increases in resistance
may be thermostats for actuating controls at se
cause increases in frequency. The constants of
lected Wet bulb temperatures, or may be thermom
the circuit are so adjusted that the frequency
eters for indicating wet bulb temperatures, or
meter i5 may be calibrated to read Wet bulb tem
peratures and to actuate controls at a predeter- ' ‘ may be combined thermostats and thermometers.
' While embodiments of the invention have been
mined wet bulb temperature.
described for the purpose of illustration, it should
The oscillator circuit of Fig. 14 is a conven
be understood that the invention is not limited
tional, relaxation type oscillator. The hygro
to the exact apparatus, arrangements of ap
scopic resistor 85 and the resistor 86, the resist
paratus and circuits illustrated, as modiñcations
ance of which is-adjusted by the bellows Si of
thereof may be suggested by those skilled in the
.the thermometer 88, are connected in series in
art without departure from the essence of the
the control grid circuit of the thermionic tube
invention.
'
B9.
What is claimed is:
The resistors 9@ and Si are limiting resistors
l. A device responsive to changes in the wet
and the condenser 9| is the feedback condenser.
bulb temperature of air, comprising an electric
The resistance of the resistor 35 decreases with
circuit, means in said circuit responsive to humid
humidity increases and the resistance of the re
ity increases in the air for varying the electrical
sistor 86 increases with dry bulb temperature in
impedance of said circuit conformably with
creases. The sum of the resistances of the re
changes in the humidity of the air, and means in
sistors 85 and 55 determines the frequency of
said circuit responsive to dry bulb Itemperature
osclllation'of the tube 89 and is an indication
increases in the air for oppositely varying the
of the wet bulb temperature. The output of the
impedance of said circuit conformably with
-tube $5 may beampliñed by the audio ampliñer
changes in the dry bulb temperature of the air.
'92 to which the frequency meter 93 is connected
2. A device responsive to changes in the wet
With reference to Fig. ‘11, the hygroscopic re
sistor 50, the variable resistor 5i adjusted by the
thermometer 55, the auxiliary variable resistor
2,412,782
’ bulb temperature of air, lcomprising an electric
circuit, means in said circuit responsive to humid
ity changes in the air for decreasing the electri
10'
changes in the air for cDpOsitely changing the
strength of said current conformably with in
creases in the dry bulb temperature of the air.
cal impedance of said circuit coniormably with
8. A device responsive to changes in the wet
increases in the humidity of the air, and means Cn bulb temperatureof air, comprising means in
in said circuit responsive to dry bulb temperature
cluding hygroscopic means exposed to the air for
changes in the air for increasing the impedance
producing an electric current iiow, the strength
thereof conformably with increases in the dry
of which varies in one direction conformably with
bulb temperature of the air.
increases in the moisture content ‘of the air, and
3. A device responsive to changes in the wet 10 means including means responsive to dry bulb
bulb temperature of air, comprising an electric
temperature changes in the air for varying the
circuit, means providing an electric capacity in
strength of said current now in the opposite di
said circuit, means including means responsive
rection conformably with increases in the dry
to humidity changes in the air for varying the
bulb temperature oi the air.
, capacitive reactance of said capacity conform 1.5
9. A device responsive to changes in the wet
ably with increases in the humidity of the air,
bulb temperature of air, comprising an electric
and means including means responsive to dry bulb
temperature changes in the air for oppositely
condenser, means including means responsive to
humidity changes in the air for increasing the
varying the capacitive reactance of said capacity
capacity of said condenser conformably with in
conformably with increases in the dry bulb tem 20 creases in themoisture content of the air, and
perature of the air.
means exposed to the air for decreasing the ca
4. A device responsive to changes in the wet
pacity of said condenser coni’ormably with in
bulb temperature of air, comprising an electric
creases in the dry bulb temperature of the air.
circuit, means in said circuit responsive to hu
10. A device responsive to changes in the wet
midity changes in the air for varying the resist 25 bulb temperature of air, comprising means for
ance of said circuit conformably with increases in
producing an alternating electric current, means
the humidity of the air, and means in said cir
including hygroscopic means exposed to the air
cuit responsive to dry bulb temperature changes
for varying the frequency of said current con
in the air for oppositely varying the resistance
formably with moisture increases in the air, and
of said circuit conformably with increases in the 30 means including means responsive to dry bulb
dry bulb temperature of the air.
temperature changes of the air for oppositely
5. A device responsive to'changes in the wet
varying the frequency of said current conform
bulb temperature of air, comprising an electric
ably with increases in the dry bulb temperature
circuit, a resistor in said circuit, means respon
of the air'.
sive to humidity changes in the air for decreas 35
11. A device responsive to changes in the wet
ing the resistance of said resistor conformably
bulb temperature oi' air, comprising means for
with increases in the humidity of the air, a sec
' producing an alternating electric current, means ,
ond resistor in said circuit, and means responsive
including hygroscopic means exposed to the air
to dry bulb temperature changes in the air for
for decreasing the frequency of said current con
increasing the resistance of said second resistor 40 formably with increases in the moisture content
conformably with increases in the dry bulb tem
of the air, and means including means responsive
perature of the air.
to dry bulb temperature changes of the air for
6. A device responsive to changes in the wet
increasing the frequency of said current con
bulb temperature of air, comprising an electric
formably with increases in the dry bulb tempera
circuit. an electric resistor in said circuit exposed 45 ture of the air.
to the air and having a resistance which increases
12. A device responsive to changes in the wet
conformably with increases in the dry bulb teln-bulb temperature of air, comprising an electric
perature of the air, and means in said circuit re
circuit. a pair of resistors in series in said circuit.
sponsive to humidity changes in the air for de
means responsive to changes in the humidity of
creasing the resistance of said circuit conform 50 the air for decreasing the resistance of one of
ably with increases in the humidity of the air.
said resistors conformably with increases in the
'1. A device responsive to changes in the wet
humidity of the air. and means responsive to
bulb temperature of air, comprising means in
changes inthe dry bulb temperature of the air for
cluding means exposed to air, providing an elec
increasing the resistance of the other of said re
tric current flow, means for changing the strength 55 sistors conformabiy with increases in the dry
of said current conformably with increases in the
_ bulb temperature of the air.
moisture content of the air, and means including
means responsive to dry bulb temperature
ROBERT T.' PALMER.
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